1. Field of the Invention
The present invention relates to a developing roller, a developing device, and an image forming apparatus.
2. Description of the Related Art
Low price, space saving and simplified system are sales points of a one-component, contact development type laser printer. For such a printer to obtain a favorable image in a stable manner over a period of time, it has already been known that stable formation of a toner thin layer having uniform charge and uniform quantity on a developing roller which bears the toner thin layer on a surface thereof and rotates to supply a toner to a region being developed has become an important technology.
With a conventional developing roller, however, a toner which has passed a regulating nip abrades a surface of the developing roller as the number of printing increases, which decreases the performance of the developing roller to scrape the toner on the toner layer regulating blade. As a result, the toner is firmly fixed (sealed) on the toner layer regulating blade. One reason for the toner fixing is reduced scraping property of the developing roller, but it is largely affected by the properties of the toner itself. There are toners which are more easily fixed. Once toner fixing occurs, no more toner can pass through the region of the toner fixing, and an image which lacks a toner and appears as a white streak in the image is obtained.
In order to improve the toner fixing on the toner layer regulating blade, various techniques have been proposed. However, many of the proposals involve increased number of parts or complex developing systems. There are not many proposals to solve the problem by the surface profile of a developing roller in a simple system having a developing roller and a toner layer regulating blade.
For example, Japanese Patent Application Laid-Open (JP-A) No. 06-175476 proposes a developing roller having a surface with irregularity, where the irregularity includes asymmetric inclinations which recede with respect to the direction of rotation. This enables uniform and sufficient delivery of a toner and reduction of the contact area between a photoconductor and the toner, resulting in life extension.
However, the concave portion of the surface of the developing roller in this proposed technology is characterized in having a front rake face and a rear flank face in order to ensure raking and retaining of a toner, where the raking face rises at a sharp angle toward an upstream side with respect to the direction of rotation, and where the flank face is shallowly inclined from the downstream side with respect to the direction of rotation so that it smoothly contacts a surface of a latent image of the photoconductor to release the toner toward the downstream side with respect to the direction of rotation. This technology cannot solve the problem of a toner firmly fixed on a toner layer regulating blade.